This invention relates to a cathode ray tube having a shadow mask attached to a peripheral frame that is suspended in relation to a screen of the cathode ray tube and, particularly, to a support system for a mask-frame assembly in such a tube, which provides an improved shock handling capability.
In most cathode ray tubes (CRT""s), a peripheral frame, supporting a shadow mask, is suspended in a faceplate panel by means of springs that are welded either directly to the frame or to plates that in turn are welded to the frame. In large size tubes, it is common to use a mask-frame assembly support consisting of four springs to support a mask-frame assembly within a rectangular faceplate panel of a tube. In many recent tubes, the springs are located at the four corners of the frame to minimize twisting and shifting of the assembly within the panel. The mask-frame assembly supports are bent metal plates each of which are welded to the frame at one end and include an aperture at the other end. Each aperture engages a metal stud that is affixed in the faceplate panel sidewall.
The use of a corner support system for the support of a CRT tube shadow mask offers many advantages over an on-axis support system. However, the corner support system has the undesirable characteristic of asymmetric resistance to shock loads. CRT""s employing corner support systems typically are less capable of sustaining shock loads in the horizontal (X) direction than in the vertical (Y) direction while returning the shadow mask to within a tolerable distance of its original position.
As usually mounted on a shadow mask frame, the corner support system springs are typically flexible in the radial direction and very stiff in the tangential direction. These springs are typically mounted at the mask diagonal corners. Because the mask diagonal does not lie at 45 degrees to the X and Y axes, for example, in a tube having a 4:3 or 16:9 (X to Y) aspect ratio, the resulting system stiffness in the X and Y directions are not equal. This inequality may result in an inadequate shock load capability and misalignment of the mask apertures with respect to their nominal positions, which, in turn, causes positional errors in the landings of the electron beams. Such mislandings are commonly referred to as misregistration, and, in operating tubes, the consequences of misregistration are white field nonuniformities and color purity errors. Hence, the need exists to reduce the propensity for such misregistration.
The invention provides a CRT having a funnel sealed at one end to a faceplate panel with a luminescent screen on an interior surface thereof, a mask assembly supported within the CRT and in proximity to the screen, the faceplate panel having a plurality of sidewalls each having an inside surface. The CRT also includes a plurality of a studs, with at least one stud affixed in each of the corners of the inside surface of the sidewalls. A plurality of springs engage the corner studs, to support the mask assembly within the CRT. At least one additional stud is affixed along the inside surface of one sidewall and a shim is attached around the additional stud. On the mask assembly, at least one bracket is positioned to have a slot into which the shim is loosely engaged, thereby mitigating motion in a plane parallel to the interior sidewall.